Both suppressor and amplifier T cell activity were found to be present in lymphoid tissues other than the spleen. Significant suppression (greater than 90%) could be demonstrated following the transfer of immunologically unresponsive lymphoid cells to normal intact mice immunized with Type III pneumococcal polysaccharide; however, the degree of suppression noted differed from experiment to experiment. The variables involved in these studies are being assessed systematically, so that this experimental approach can be used to obtain information concerning the mechanism by which both types of regulatory T cells are activated during the course of an immune response.